1. First secure your master onto a flat surface - this could be an acrylic block, tile or old CD case. You can secure it with double-sided tape or sticky tack if you want to be able to remove it later, or glue with Araldite for a master that will last forever!
2. Make a wall around your object which isn't too far away from your original otherwise you will use too much silicone. In our example we used a plastic drinking cup, but you could use anything with a shiny interior. The outside of a cereal box, a plastic box, etc. Ensure the wall is sealed with sulphur free plasticene so that the silicone doesn't leak out. The finished item is called a mould box. You could choose to spray the original with release agent (such as a silicone-free beeswax furniture spray) but it is not usually necessary, especially if your mould box has a shiny interior.
3. Mark a line on the mould box about 6 or 8mm above the master. This is the level where you will pour the silicone up to.
4. Give the mould-it tubs a good shake and stir before use.
5. Calculate how much silicone you will need to measure out (see extra tips below).
6. Place a mixing cup onto a pair of accurate digital scales and set the weight on the scales to 0g.
7. Pour the required amount of Part A (Base) into the measuring cup and then top up with the same amount of Part B (Catalyst).
8. Stir slowly and thoroughly for 2-3 minutes, until the colour has combined completely.
9. Leave to stand for 2-3 minutes to help any bubbles move to the surface.
10. Pour the silicone into the mould box in a thin, steady stream (bead) from a 30mm height.
11. Gently tap the box to remove any bubbles, pop any surface bubbles with a cocktail stick and leave in a warm, dry place for around 60-90 minutes.
12. Once set, the mould box can be removed and the mould trimmed with household scissors if required.
For an easy way to work out the volume of silicone you will need some rice (yes you read that right... RICE. No, we haven't gone mad... all will become clear in just a tick). Pour the rice into the mould box to cover the master and then tip the rice into a clear plastic cup. Mark the level that the rice reaches in the cup and then pour the rice out. This will give you the total volume that you need to make the mould. (The reason why you use rice rather than water, is so that no water is left behind - water and silicone don't get on well with each other).
For a superior, bubble-free finish we recommend coating the master with a thin layer of silicone mixture before you start pouring. You can do this either with a paintbrush or by pouring some mixed silicone in on top of the original and then tipping it out again, leaving a thin layer on top of the original. This is to ensure that there are no air bubbles next to the original, which will give you lumps on your casting. You can use a straw to blow on the bubbles and burst them, and a cocktail stick to pop any large ones.
Another top bubble-removal tip is to start your pour in a corner, away from the master. This means you should avoid any bubbles appearing around your master.
Resin8 mould-it has a shore hardness of 22A - it will make a soft mould with lots of flexibility. Expect your mould to last for around 8-10 uses at a minimum, depending on the intricacy of the detail, how you look after your mould and how carefully you demould.